Light emitting device having micro epitaxial structures and manufacturing method thereof

ABSTRACT

A light emitting device includes a first substrate, a second substrate and a plurality of micro epitaxial structures. The second substrate is disposed opposite to the first substrate. The micro epitaxial structures are periodically disposed on the substrate and located between the first substrate and the second substrate. A coefficient of thermal expansion of the first substrate is CTE1, a coefficient of thermal expansion of the second substrate is CTE2, a side length of each of the micro epitaxial structures is W, W is in the range between 1 micrometer and 100 micrometers, and a pitch of any two adjacent micro epitaxial structures is P, wherein W/P=0.1 to 0.95, and CTE2/CTE1=0.8 to 1.2.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority benefit of Taiwan applicationserial no. 104129267, filed on Sep. 4, 2015. The entirety of theabove-mentioned patent application is hereby incorporated by referenceherein and made a part of this specification.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention generally relates to a semiconductor element and amanufacturing method thereof, and more particularly, to a light emittingdevice and a manufacturing method thereof.

2. Description of Related Art

In current manufacturing process of a light emitting diode (LED)structure, first of all, an epitaxial structure is formed on a growthsubstrate. The epitaxial structure includes a first-type semiconductorlayer, a light emitting layer and a second-type semiconductor layersequentially formed on the growth substrate. Subsequently, a permanentsubstrate or a temporary substrate is bonded on the second-typesemiconductor layer to form the LED structure or a LED structure to betransferred. In general, the growth substrate mainly uses a sapphiresubstrate, which has a coefficient of thermal expansion very differentfrom a coefficient of thermal expansion of the permanent substrate orthe temporary substrate. Therefore, when the epitaxial structure istransferred from the growth substrate onto the permanent substrate orthe temporary substrate, a shift phenomenon may occur under an influenceof the thermal stress to affect an alignment precision of the product orthe device.

SUMMARY OF THE INVENTION

The invention is directed to a light emitting device with a preferablealignment precision.

The invention is further directed to a manufacturing method of a lightemitting device for manufacturing the said light emitting device.

The light emitting device of the invention includes a first substrate, asecond substrate and a plurality of micro epitaxial structures. Thesecond substrate is disposed opposite to the first substrate. The microepitaxial structures are periodically disposed on the first substrateand located between the first substrate and the second substrate. Acoefficient of thermal expansion of the first substrate is CTE1, acoefficient of thermal expansion of the second substrate is CTE2, a sidelength of each of the micro epitaxial structures is W, W ranges from 1to 100 micrometers, and a pitch of any two adjacent micro epitaxialstructures is P, wherein W/P=0.1 to 0.95, and CTE2/CTE1=0.8 to 1.2.

In one embodiment of the invention, when W/P ranges from 0.1 to 0.6,CTE2/CTE1=0.9 to 1.1.

In one embodiment of the invention, the first substrate and the secondsubstrate have approximately the same size and shape.

In one embodiment of the invention, the light emitting device furtherincludes a first bonding layer disposed between the micro epitaxialstructures and the second substrate, and the second substrate is fixedon the first substrate through the first bonding layer.

In one embodiment of the invention, a side of the micro epitaxialstructures directly contacts the first substrate, and the first bondinglayer encapsulates each of the micro epitaxial structures.

In one embodiment of the invention, the first bonding layer fills upgaps between micro epitaxial structures.

In one embodiment of the invention, the light emitting device furtherincludes an insulating material, which fills up gaps between microepitaxial structures.

In one embodiment of the invention, the light emitting device furtherincludes a second bonding layer disposed between the micro epitaxialstructures and the first substrate, and the micro epitaxial structuresare fixed on the first substrate through the second bonding layer.

In one embodiment of the invention, the second bonding layer fills upgaps between micro epitaxial structures.

In one embodiment of the invention, a current density at the highestpeak value of an external quantum efficiency curve of each of the microepitaxial structures is below 2 A/cm².

In one embodiment of the invention, a defect density of each of themicro epitaxial structures is less than 10⁸/cm².

The manufacturing method of the light emitting device of the inventionincludes the following steps. A first substrate is provided. Acoefficient of thermal expansion of the first substrate is CTE1, and thefirst substrate has a plurality of micro epitaxial structuresperiodically disposed thereon. A side length of each of the microepitaxial structures is W, W ranges from 1 to 100 micrometers, and apitch of any two adjacent micro epitaxial structures is P, whereinW/P=0.1 to 0.95. A bonding material is provided on the first substrate.A second substrate is disposed opposite to the first substrate, themicro epitaxial structures are located between the first substrate andthe second substrate, and the second substrate is bonded with the microepitaxial structures through the bonding material, wherein a coefficientof thermal expansion of the second substrate is CTE2, and CTE2/CTE1=0.8to 1.2. The first substrate and the micro epitaxial structures areseparated.

In one embodiment of the invention, when W/P ranges from 0.1 to 0.6,CTE2/CTE1=0.9 to 1.1.

In one embodiment of the invention, the bonding material, after beingprovided on the micro epitaxial structures via a spin coating method, isbonded with the second substrate.

In one embodiment of the invention, the spin coating method is multipletimes of spin coating.

In one embodiment of the invention, the bonding material fills up gapsbetween the micro epitaxial structures.

In one embodiment of the invention, the bonding material is provided onthe micro epitaxial structures via a film coating method and then bondedwith the second substrate via a hot pressing method.

In one embodiment of the invention, the micro epitaxial structures arefixed on the first substrate through an adhesive layer.

In one embodiment of the invention, the adhesive layer fills up gapsbetween the micro epitaxial structures.

In view of the above, since the coefficient of thermal expansion (i.e.,CTE1) of the first substrate and the coefficient of thermal expansion(i.e., CTE2) of the second substrate of the light emitting device of theinvention are related to the side length (i.e., W) and the pitch (i.e.,P) of the micro epitaxial structures, when W ranges from 1 to 100micrometers and W/P=0.1 to 0.95, CTE2/CTE1=0.8 to 1.2. That is, thelight emitting device of the invention adopts the first substrate andthe second substrate which have similar coefficients of thermalexpansion. Therefore, in the substrate transfer process, when the microepitaxial structures are about to be transferred from the firstsubstrate onto the second substrate, the micro epitaxial structures willnot produce a displacement due to a variation between the coefficientsof thermal expansion of the first substrate and the second substrate. Asa result, the micro epitaxial structures can be transferred between thefirst substrate and the second substrate with a fixed pitch, and therebycan have a preferable alignment precision.

In order to make the aforementioned and other features and advantages ofthe invention comprehensible, several exemplary embodiments accompaniedwith figures are described in detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of the invention, and are incorporated in and constitute apart of this specification. The drawings illustrate embodiments of theinvention and, together with the description, serve to explain theprinciples of the invention.

FIG. 1A is cross-sectional diagram illustrating a light emitting deviceaccording to an embodiment of the invention.

FIG. 1A′ is cross-sectional diagram illustrating a light emitting deviceaccording to another embodiment of the invention.

FIG. 1B is cross-sectional diagram illustrating a light emitting deviceaccording to another embodiment of the invention.

FIG. 1C is cross-sectional diagram illustrating a light emitting deviceaccording to another embodiment of the invention.

FIG. 1D is cross-sectional diagram illustrating a light emitting deviceaccording to another embodiment of the invention.

FIG. 2A is cross-sectional diagram illustrating a light emitting deviceaccording to another embodiment of the invention.

FIG. 2B is cross-sectional diagram illustrating a light emitting deviceaccording to another embodiment of the invention.

FIG. 2C is cross-sectional diagram illustrating a light emitting deviceaccording to another embodiment of the invention.

FIG. 3A(a) to FIG. 3D(c) are cross-sectional diagrams respectivelyillustrating manufacturing methods of light emitting devices accordingto several embodiment of the invention.

DESCRIPTION OF THE EMBODIMENTS

FIG. 1A is cross-sectional diagram illustrating a light emitting deviceaccording to an embodiment of the invention. Referring to FIG. 1A, inthe present embodiment, a light emitting device 100 a includes a firstsubstrate 110, a second substrate 140 a and a plurality of microepitaxial structures 120. The second substrate 140 a is disposedopposite to the first substrate 110. The micro epitaxial structures 120are periodically disposed on the first substrate 110 and located betweenthe first substrate 110 and the second substrate 140 a. A coefficient ofthermal expansion of the first substrate 110 is CTE1, a coefficient ofthermal expansion of the second substrate 140 a is CTE2, a side lengthof each of the micro epitaxial structures 120 is W, W ranges from 1 to100 micrometers, and a pitch of any two adjacent micro epitaxialstructures 120 is P, wherein W/P=0.1 to 0.95, and CTE2/CTE1=0.8 to 1.2.Herein, sizes and shapes of the first substrate 110 and the secondsubstrate 140 a are not particularly limited. It is to be noted that,the pitch P is defined by a distance between the centrelines of any twoadjacent micro epitaxial structures 120.

In detail, the first substrate 110 of the present embodiment is, forexample, a sapphire substrate, wherein the micro epitaxial structures120 directly contact the first substrate 110, and the first substrate110 is a growth substrate of the micro epitaxial structures 120. Themicro epitaxial structures 120 are periodically disposed on the firstsubstrate 110, wherein each of the micro epitaxial structures 120includes a first type semiconductor layer 122, an active layer 124 and asecond type semiconductor layer 126. The active layer 124 is locatedbetween the first type semiconductor layer 122 and the second typesemiconductor layer 126. In each of the micro epitaxial structures 120of the present embodiment, the first type semiconductor layer 122 is,for example, a P-type semiconductor layer, the second type semiconductorlayer 126 is, for example, a N-type semiconductor layer, and the activelayer 124 is a multiple quantum well (MQW) structure. In other notembodiment (not shown), it may also be that the first type semiconductorlayer 122 is, for example, e a N-type semiconductor layer, the secondtype semiconductor layer 126 is, for example, is a P-type semiconductorlayer, and the active layer 124 is a MQW structure, but the invention isnot limited thereto. Particularly, a current density at the highest peakvalue of an external quantum efficiency curve of each of micro epitaxialstructures 120 of the present embodiment is, preferably, below 2 A/cm²,and more preferably, ranges from 0.5 A/cm² to 1.5 A/cm². Namely, thelight emitting device 100 a of the present embodiment is adapted to beoperated under a condition of low current density. On the other hand,each of the micro epitaxial structures 120 of the present embodiment mayserve as a sub-pixel in a display. More specifically, the microepitaxial structures 120 of the present embodiment have different sizesthan epitaxial structures of the conventional light emitting diodes thatare commonly used. In detail, a side length of each of the epitaxialstructures of the conventional light emitting diodes epitaxialstructures ranges from 0.2 mm to 1 mm, while the side length of each ofthe micro epitaxial structures 120 of the present embodiment ranges from1 micrometer to 100 micrometers; and preferably, the side length of eachof the micro epitaxial structures 120 ranges from 3 micrometers to 40micrometers. In addition, a defect density of each of the microepitaxial structures 120 of the present embodiment is also less;preferably, the defect density of each of the micro epitaxial structures120 is less than 10⁸/cm²; and more preferably, the defect density ofeach of the epitaxial structures 120 ranges from 5×10⁵/cm² to 10⁸/cm².

Moreover, the light emitting device 100 a of the present embodimentfurther includes a plurality of bonding pads 130 a, wherein the bondingpads 130 a are respectively disposed on the micro epitaxial structures120 and located on surfaces of the micro epitaxial structures 120 whichare relatively distant to the first substrate 110. That is to say, thesurface of each of the micro epitaxial structures 120 that is relativelydistant to the first substrate 110 is disposed with one bonding pad 130a. In order to protect the micro epitaxial structures 120, the lightemitting device 100 a of the present embodiment may further include aplurality of insulating layers 170, wherein the insulating layers 170respectively encapsulate sides of the micro epitaxial structures 120,and the insulating layers 170 expose the bonding pads 130 a, so as toeffectively protect the edges of the micro epitaxial structures 120 andprevent water vapor and oxygen invasions, and thereby effectivelyenhance the product reliability of the overall light emitting device 100a. Herein, a material of the insulating layers 170 is, for example,silicon dioxide, alumina, silicon nitride or a combination thereof.Moreover, in another embodiment, referring to FIG. 1A′, the firstsubstrate 110′ and the second substrate 140 a′ of the light emittingdevice 100 a′ may have approximately the same size and shape, so thatthe first substrate 110′ and the second substrate 140 a′ can havesimilar boundary conditions, thereby effectively enhancing a transferyield of the micro epitaxial structures 120 at the edges.

Sine the coefficient of thermal expansion (i.e., CTE1) of the firstsubstrate 110 and the coefficient of thermal expansion (i.e., CTE2) ofthe second substrate 140 a of the light emitting device 100 a of thepresent embodiment are related to the side length (i.e., W) and thepitch (i.e., P) of the micro epitaxial structures 120, when W/P=0.1 to0.95, CTE2/CTE1=0.8 to 1.2. Preferably, when W/P ranges from 0.1 to 0.6,CTE2/CTE1=0.9 to 1.1. That is, the light emitting device 100 a of thepresent embodiment uses the first substrate 110 and the second substrate140 a which have similar coefficients of thermal expansion, and thus ina substrate transfer process, such as when transferring the microepitaxial structures 120 from the first substrate 110 onto the secondsubstrate 140 a, the micro epitaxial structures 120 will not produce adisplacement due to differences between the coefficients of thermalexpansion of the first substrate 110 and the second substrate 140 a. Asa result, the micro epitaxial structures 120 can be transferred betweenthe first substrate 110 and the second substrate 140 a with a fixedpitch, and thus can have a preferable alignment precision.

In order to further prevent the micro epitaxial structures 120 frombeing dislocated during the substrate transfer process, the lightemitting device 100 a of the present embodiment may also furtherincludes a first bonding layer 150 a disposed between the microepitaxial structures 120 and the second substrate 140 a, and the secondsubstrate 140 a is fixed on the first substrate 110 through the firstbonding layer 150 a. As shown in FIG. 1A, the first bonding layer 150 ais disposed on the second substrate 140 a, and the first bonding layer150 a directly contacts the bonding pads 130 a, which are disposed onthe micro epitaxial structures 120, and is substantially a planarstructure. In other words, a gap G between any two adjacent microepitaxial structures 120 is substantially an air gap.

Certainly, the invention does not limit the structure and form of thefirst bonding layer 150 a. In other embodiment, referring to FIG. 1B, alight emitting device 100 b of the present embodiment is similar to thelight emitting device 100 a of FIG. 1A, whereby differences therebetweenmerely lie in that: a side of the micro epitaxial structures 120 of thelight emitting device 100 b of the present embodiment directly contactsthe first substrate 110, the first bonding layer 150 b encapsulates eachof the micro epitaxial structures 120, and the first bonding layer 150 bfills up the gaps G between the micro epitaxial structures 120. Morespecifically, since a bond force between the micro epitaxial structures120 and the first substrate 110 (i.e., the growth substrate) is large,in order for the first substrate 110 to be effectively separated fromthe micro epitaxial structures 120 during the subsequent process and tofixe the pitch between the micro epitaxial structures 120, the firstbonding layer 150 b must cover around and on the top surfaces of themicro epitaxial structures 120, such that the first bonding layer 150 bon the top surfaces of the micro epitaxial structures 120 is used tobond with the second substrate 140 a while the first bonding layer 150 bused to fill the gaps G is used for fixing the pitch of the microepitaxial structures 120, wherein the first substrate 110 is laterremoved during the subsequent process through laser lift-off (LLO).

Furthermore, the gaps G of micro epitaxial structures 120 of the lightemitting device 100 b of the invention may also not be filled with thefirst bonding layer 150 b. In other embodiment, referring to FIG. 1C, alight emitting device 100 c of the present embodiment is similar to thelight emitting device 100 a of FIG. 1A, whereby differences therebetweenmerely lie in that: the light emitting device 100 c of the presentembodiment further includes an insulating material 155, which fills upthe gaps G between the micro epitaxial structures 120 and directlycontacts the first bonding layer 150 a and the first substrate 110.Herein, since the purposes of the first bonding layer 150 a and theinsulating material 155 are different, material properties of theinsulating material 155 may be different from that of the first bondinglayer 150 a. More specifically, the first bonding layer 150 a is usedfor bonding the second substrate 140 a, so that the second substrate 140a can be bonded with the micro epitaxial structures 120 through thefirst bonding layer 150 a, while the insulating material 155 is used forfixing the pitch of the micro epitaxial structures 120. A viscosity ofthe insulating material 155 is less than a viscosity of the firstbonding layer 150 a, the insulating material 155 with low viscosity hasbetter filling effect and can more accurately fix the pitch of the microepitaxial structures 120; and the first bonding layer 150 a with highviscosity has a greater bonding force with the micro epitaxialstructures 120 and the second substrate 140 a and can securely fix themicro epitaxial structures 120 on the second substrate 140 a. In view ofthe above, by using the first bonding layer 150 a and insulatingmaterial 155 in coordination, the micro epitaxial structures 120 can betransferred onto the second substrate 140 a more accurately. On theother hand, the invention does not limit the structures and forms of thebonding pads 130 a, the second substrate 140 a and the first bondinglayer 150 a. Referring to FIG. 1D, a light emitting device 100 d of thepresent embodiment is similar to the light emitting device 100 a of FIG.1A, whereby a difference therebetween merely lies in that: bonding pads130 d of the light emitting device 100 d of the present embodimentinclude a plurality of first bonding pads 132 d and a plurality ofsecond bonding pads 134 d, and the surface of each of the microepitaxial structures 120 that is relative distant to the first substrate110 is disposed with one first bonding pad 132 d and one second bondingpad 134 d. The first bonding pads 132 d and the first type semiconductorlayers 122 of the micro epitaxial structures 120 are structurally andelectrically connected, and the second bonding pads 134 d and the secondtype semiconductor layers 126 of the micro epitaxial structures 120 arestructurally and electrically connected. Herein, each of the microepitaxial structures 120 and the bonding pad 130 d thereon can define ahorizontal light-emitting diode chip. Further, the second substrate 140d of the present embodiment is substantially a conductive substrate, andthe second substrate 140 d has a plurality of conductive vias structures142. The first bonding pads 132 d and the second bonding pads 134 dstructurally and electrically connect the conductive vias structures142. Furthermore, the first bonding layer 150 d of the presentembodiment is substantially a patterned bonding layer, which is onlylocated between the conductive vias structures 142 and the first bondingpads 132 d and between the conductive vias structures and the secondbonding pads 134 d. The gap G between any two adjacent micro epitaxialstructures 120 is substantially an air gap.

In addition, the invention does not limit the first substrate 110 to beonly a growth substrate. Referring to FIG. 2A, a light emitting device100 e of the present embodiment is similar to the light emitting device100 a of FIG. 1A, wherein a differently merely lies in that: a firstsubstrate 110 e of the present embodiment is not a growth substrate buta temporary substrate, and thus the light emitting device 100 e of thepresent embodiment may further includes a second bonding layer 160located between the micro epitaxial structures 120 and the firstsubstrate 110 e, and the micro epitaxial structures 120 are fixed on thefirst substrate 110 e through the second bonding layer 160. Herein, asshown in 2A, the micro epitaxial structures 120 directly contact thesecond bonding layer 160, and the gap G between any two adjacent microepitaxial structures 120 is substantially an air gap.

In another embodiment, referring to FIG. 2B, a light emitting device 100f of the present embodiment is similar to light emitting device 100 e ofFIG. 2A, whereby a difference therebetween merely lies in that: thelight emitting device 100 f of the present embodiment further includesan insulating material 155′ disposed between the first substrate 110 eand the second substrate 140 a and filling up the gaps G between themicro epitaxial structures 120. Herein, the material of the insulatingmaterial 155′ can be the same as or different from the material of thefirst bonding layer 150 a and the material of the second bonding layer160, wherein the invention is not limited thereto.

Also, in another embodiment, referring to FIG. 2C, a light emittingdevice 100 g of the present embodiment is similar to the light emittingdevice 100 e of FIG. 2A, whereby differences between the two merely liein that: bonding pads 130 d of the light emitting device 100 g of thepresent embodiment include a plurality of first bonding pads 132 d and aplurality of second bonding pads 134 d, and the surface of each of themicro epitaxial structures 120 that is relatively distant to the firstsubstrate 110 e has one first bonding pad 132 d and one second bondingpad 134 d disposed thereon. The first bonding pads 132 d and the firsttype semiconductor layers 122 of the micro epitaxial structures 120 arestructurally and electrically connected, and the second bonding pads 134d and the second type semiconductor layers 126 of the micro epitaxialstructures 120 are structurally and electrically connected. Herein, eachof the micro epitaxial structures 120 and the bonding pad 130 d thereoncan define a horizontal light-emitting diode chip. In addition, thesecond bonding layer 160′ of the present embodiment fills up the gaps Gbetween the micro epitaxial structures 120 and directly contacts thefirst bonding layer 150 a and the first substrate 110 e.

In terms of processing, a manufacturing method of the light emittingdevice of the present embodiment can firstly be referred to FIG. 3A(a).A first substrate 110 is provided, wherein a coefficient of thermalexpansion of the first substrate 110 is CTE1, the first substrate 110has a plurality of micro epitaxial structures 120 periodically disposedthereon, a side length of each of the micro epitaxial structures 120 isW, W ranges from 1 to 100 micrometers, and a pitch between two adjacentmicro epitaxial structures 120 is P, and W/P=0.1 to 0.95. In detail, thefirst substrate 110 is a sapphire substrate, and after an epitaxial filmis grown on the first substrate 110 through metalorganic chemical vapordeposition, the epitaxial film is formed into the micro epitaxialstructures 120 via a semiconductor processing method. Thus, the microepitaxial structures 120 are directly formed on the first substrate 110.In other words, the first substrate 110 is a growth substrate of themicro epitaxial structures 120. Each of the micro epitaxial structures120 includes a second type semiconductor layer 126, an active layer 124and a first type semiconductor layer 122 sequentially stacked on thefirst substrate 110.

As shown in FIG. 3A(a), in the present embodiment, the micro epitaxialstructures 120 further includes a plurality of bonding pads 130 adisposed thereon, wherein the bonding pads 130 a are respectively formedon the micro epitaxial structures 120 and located on the surfaces of themicro epitaxial structures 120 that are relatively distant to the firstsubstrate 110. That is to say, the surface of each of the microepitaxial structures 120 that is relatively distant to the firstsubstrate 110 is disposed with one bonding pad 130 a. Herein, each ofthe micro epitaxial structures 120 of the present embodiment and each ofthe bonding pads 130 a can define a vertical light-emitting diode chip.In order to effectively protect the micro epitaxial structures 120, themanufacturing method of the light emitting device of the presentembodiment further includes to form a plurality of insulating layers170, wherein the insulating layers 170 respectively encapsulate thesides of the micro epitaxial structures 120, and the insulating layers170 expose the bonding pads 130 a, so as to effectively effect the edgesof the micro epitaxial structures 120, thereby preventing the watervapor and oxygen invasions and effectively enhancing the productreliability. Herein, the material of the insulating layers 170 may, forexample, be alumina, silicon dioxide, silicon nitride or a combinationthereof.

The invention does not limit the structure and form of the bonding pads130 a. In other embodiment, as shown in FIG. 3A(b), bonding pads 130 dof the present embodiment include a plurality of first bonding pads 132d and a plurality of second bonding pads 134 d, and the surface of eachof the micro epitaxial structures 120 that is relatively distant to thefirst substrate 110 is disposed with one first bonding pad 132 d and onesecond bonding pad 134 d thereon. The first bonding pads 132 d and thefirst type semiconductor layer 122 of the micro epitaxial structures 120are structurally and electrically connected, and the second bonding pads134 d and the second type semiconductor layers 126 of the microepitaxial structures 120 are structurally and electrically connected.Herein, each of the micro epitaxial structures 120 and the bonding pad130 d thereon can define a lateral light-emitting diode chip. Theinsulating layers 170 respectively encapsulate the sides of the microepitaxial structures 120, and the insulating layers 170 expose thebonding pads 130 d, so as to effectively protect the edges of the microepitaxial structures 120, thereby preventing the water vapor and oxygeninvasions and effectively enhancing the product reliability.

The invention does not limit that the first substrate 110 to be only agrowth substrate. In another embodiment, as shown in FIG. 3A(c), a firstsubstrate 110 e is a temporary substrate, and thus the micro epitaxialstructures 120 may be fixed on the first substrate 110 e through anadhesive layer (i.e., the second bonding layer 160).

Next, referring to FIG. 3B(a), the bonding material (i.e., the firstbonding layer 150 a) is provided on the first substrate 110. Herein, thefirst bonding layer 150 a covers on the micro epitaxial structures 120via a film coating method, directly contacts the bonding pads 130 adisposed on the micro epitaxial structures 120, and is substantially aplanar structure. In other words, the gap G between any two adjacentmicro epitaxial structures 120 is substantially the air gap.

In another embodiment, referring to FIG. 3B(b), the bonding material(i.e., the first bonding layer 150 b) is covered on the micro epitaxialstructures 120 via the spin coating method through performing one timeof spin coating, wherein the first bonding layer 150 b fills up the gapsG between the micro epitaxial structures 120, so as to prevent theepitaxial structures 120 from being dislocated during the subsequentsubstrate transfer process.

In another embodiment, referring to FIG. 3B(c), the bonding material(i.e., the first bonding layer 150 a and the insulating material 155) isalso formed on the first substrate 110 via the spin coating methodthrough performing multiple times of spin coating. Herein, theinsulating material 155 fills up the gaps G between the micro epitaxialstructures 120 and directly contacts the first bonding layer 150 a andthe first substrate 110, so as to prevent the epitaxial structures 120from being dislocated during the subsequent substrate transfer process.Herein, the material of the insulating material 155 can be differentfrom that of the first bonding layer 150 a.

Certainly, the invention does not limit the structure and form of thebonding material. In another embodiment, referring to FIG. 3B(d), thebonding material (i.e., the first bonding layer 150 d) may also be apatterned bonding layer disposed on the first bonding pads 132 d and thesecond bonding pads 134 d of the bonding pads 130 d. Herein, the bondingmaterial with a planar structure is firstly formed to cover on the microepitaxial structures 120 via a film coating method, and is then formedinto the patterned bonding layer through an etching process.

In another embodiment, referring to FIG. 3B(e), when the first substrate110 e is not a growth substrate, the micro epitaxial structures 120 arefixed on the first substrate 110 e through an adhesive layer (i.e., thesecond bonding layer 160′) and the adhesive layer (i.e., the secondbonding layer 160′) fills up the gaps G between the micro epitaxialstructures 120. Herein, the adhesive layer (i.e., the second bondinglayer 160′) and the bonding material (i.e., the first bonding layer 150a) may be formed on the first substrate 110 by performing multiple timesof spin coating. The bonding material (i.e., the first bonding layer 150a) is disposed on the adhesive layer (i.e., the second bonding layer160′) and directly contacts the first bonding pads 132 d, the secondbonding pads 134 d and the adhesive layer (i.e., the second bondinglayer 160′).

Next, referring to FIG. 3C(a) and FIG. 3C(b), the second substrate 140 ais disposed opposite to the first substrate 110, 110 e, the microepitaxial structures 120 are located between the first substrate 110,110 e and the second substrate 140 a, and the second substrate 140 a isbonded with the micro epitaxial structures 120 through the bondingmaterial (i.e., the first bonding layer 150 a), wherein the coefficientof thermal expansion of the second substrate 140 a is CTE2, andCTE2/CTE1=0.8 to 1.2. Preferably, when W/P ranges from 0.1 to 0.6,CTE2/CTE1=0.9 to 1.1. Herein, the sizes and the shapes of the firstsubstrate 110, 110 e and the second substrate 140 a are not particularlylimited, and the manufacturing of the light emitting device 100 c, 100 eis completed. In addition, in other embodiment, the first substrate 110,110 e and the second substrate 140 a may have approximately the samesize and the same shape (please refer to the structures and forms of thefirst substrate 110′ and the second substrate 140 a′ in FIG. 1A′), sothat the first substrate 110, 110 e and the second substrate 140 a canhave the similar boundary conditions, thereby effectively increasing thetransfer yield of the micro epitaxial structures 120 at the edges.

In another embodiment, referring to FIG. 3C(c), the second substrate 140d of the present embodiment may also be a conductive substrate, thesecond substrate 140 d may have a plurality of conductive viasstructures 142, and the first bonding pads 132 d and the second bondingpads 134 d are structurally and electrically connected with theconductive vias structures 142. Furthermore, the bonding material (i.e.,the first bonding layer 150 d) of the present embodiment is only locatedbetween the conductive vias structures 142 and the first bonding pads132 d and between the conductive vias structures 142 and the secondbonding pads 134 d, and the micro epitaxial structures 120 are connectedwith the second substrate 140 d through the bonding material (i.e., thefirst bonding layer 150 d). At this moment, the manufacturing of thelight emitting device 100 d is completed.

Finally, referring to FIG. 3D(a) and FIG. 3D(b), when the firstsubstrate 110 is a sapphire substrate, the first substrate 110 may beseparated from the micro epitaxial structures 120 by means of laserlift-off (LLO). Otherwise, referring to FIG. 3D(c), when the firstsubstrate 110 e is not a growth substrate of the micro epitaxialstructures 120 but a temporary substrate, the first substrate 110 e andthe bonding material (i.e., the second bonding layer 160) can also bedirectly removed by means of LLO or liquid exfoliation.

Since the coefficient of thermal expansion (i.e. CTE1) of the firstsubstrate 110, 110 e and the coefficient of thermal expansion (i.e.CTE2) of the second substrate 140 a, 140 d of the light emitting device100 c, 100 d, 100 e of the present embodiment are related to the sidelength (i.e. W) and the pitch (i.e. P) of the micro epitaxial structures120, when W/P=0.1 to 0.95, CTE2/CTE1=0.8 to 1.2. That is, the lightemitting device 100 c, 100 d, 100 e of the present embodiment adopts thefirst substrate 110, 110 e and the second substrate 140 a, 140 d whichhave similar coefficients of thermal expansion, and thus in thesubstrate transfer process, such as when transferring the microepitaxial structures 120 from the first substrate 110, 110 e onto thesecond substrate 140 a, 140 d, the micro epitaxial structures 120 willnot produce a displacement due to a variation between the coefficientsof thermal expansion of the first substrate 110, 110 e and the secondsubstrate 140 a, 140 d. As a result, the micro epitaxial structures 120can be transferred between the first substrate 110, 110 e and the secondsubstrate 140 a, 140 d with a fixed pitch, and thus can have apreferable alignment precision.

In summary, since the coefficient of thermal expansion (i.e., CTE1) ofthe first substrate and the coefficient of the thermal expansion (i.e.,CTE2) of the second substrate of the light emitting device of theinvention are related to the side length (i.e., W) and the pitch (i.e.,P) of the micro epitaxial structures, when W ranges from 1 to 100micrometers and W/P=0.1 to 0.95, CTE2/CTE1=0.8 to 1.2. That is, thelight emitting device of the invention adopts the first substrate andthe second substrate which have similar coefficients of thermalexpansion. Therefore, in the substrate transfer process, when the microepitaxial structures are about to be transferred from the firstsubstrate onto the second substrate, the micro epitaxial structures willnot produce a displacement due to a variation between the coefficientsof thermal expansion of the first substrate and the second substrate. Asa result, the micro epitaxial structures can be transferred between thefirst substrate and the second substrate with a fixed pitch, and therebycan have the preferable alignment precision.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the structure of the presentinvention without departing from the scope or spirit of the invention.In view of the foregoing, it is intended that the present inventioncover modifications and variations of this invention provided they fallwithin the scope of the following claims and their equivalents.

What is claimed is:
 1. A light emitting device, comprising: a firstsubstrate; a second substrate, disposed opposite to the first substrate;and a plurality of micro epitaxial structures, periodically disposed onthe first substrate and bonded with the second substrate via athermocompression bonding method, wherein a coefficient of thermalexpansion of the first substrate is CTE1, a coefficient of thermalexpansion of the second substrate is CTE2, a side length of each of themicro epitaxial structures is W, W ranges from 1 to 100 micrometers, anda pitch of any two adjacent micro epitaxial structures is P, whereinW/P=0.1 to 0.95, and CTE2/CTE1=0.8 to 1.2; a first bonding layer,disposed between the micro epitaxial structures and the secondsubstrate, and the second substrate is fixed on the first substratethrough the first bonding layer; a second bonding layer, disposedbetween the micro epitaxial structures and the first substrate, and themicro epitaxial structures are fixed on the first substrate through thesecond bonding layer; and wherein a side of each of the micro epitaxialstructures directly contacts the first bonding layer, and the secondbonding layer encapsulates each of the micro epitaxial structures. 2.The light emitting device as recited in claim 1, wherein when W/P rangesfrom 0.1 to 0.6, CTE2/CTE1=0.9 to 1.1.
 3. The light emitting device asrecited in claim 1, wherein the first substrate and the second substratehave approximately the same size and shape.
 4. The light emitting deviceas recited in claim 1, wherein the first bonding layer fills up gapsbetween the micro epitaxial structures.
 5. The light emitting device asrecited in claim 1, further comprising: an insulating material, fillingup gaps between the micro epitaxial structures.
 6. The light emittingdevice as recited in claim 1, wherein the second bonding layer fills upgaps between micro epitaxial structures.
 7. The light emitting device asrecited in claim 1, wherein a current density at the highest peak valueof an external quantum efficiency curve of each of the micro epitaxialstructures is below 2 A/cm².
 8. The light emitting device as recited inclaim 1, wherein a defect density of each of the micro epitaxialstructures is less than 10⁸/cm².
 9. A manufacturing method of a lightemitting device, comprising: providing a first substrate, a coefficientof thermal expansion of the first substrate being CTE1, and the firstsubstrate having a plurality of micro epitaxial structures periodicallyfixed on the first substrate through an adhesive layer, wherein theadhesive layer fills up gaps between micro epitaxial structures, whereina side length of each of the micro epitaxial structures is W, W rangesfrom 1 to 100 micrometers, a pitch of any two adjacent micro epitaxialstructures is P, and W/P=0.1 to 0.95; providing a bonding materialcovered on the micro epitaxial structures via a film coating method onthe first substrate; disposing a second substrate opposite to the firstsubstrate, the micro epitaxial structures being located between thefirst substrate and the second substrate, and the second substrate beingbonded with the micro epitaxial structures through the bonding materialvia a thermocompression bonding method, wherein a coefficient of thermalexpansion of the second substrate is CTE2, and CTE2/CTE1=0.8 to 1.2; andseparating the first substrate from the micro epitaxial structures. 10.The manufacturing method of the light emitting device as recited inclaim 9, wherein when W/P ranges from 0.1 to 0.6, CTE2/CTE1=0.9 to 1.1.11. The manufacturing method of the light emitting device as recited inclaim 9, wherein the bonding material, after being covered on the microepitaxial structures via a spin coating method, is bonded with thesecond substrate.
 12. The manufacturing method of the light emittingdevice as recited in claim 11, wherein the spin coating method ismultiple times of spin coating.
 13. The manufacturing method of thelight emitting device as recited in claim 11, wherein the bondingmaterial fills up gaps between micro epitaxial structures.